Any suggestions on what size of exaust to use for my Aero. I think 2 1/2" would be best, any thoughts?
Thanks

 

I agree that 2-1/2 would be the best compromise for this system, unless you are going for Y duals, then I would go 2-1/2 to 3" back to 2-1/2" out the back.

 

Dual or single?

 

Ok, lets looka t this more closely. A 2 1/2 would be good for the 4.0, but is too large for a 3.0

Single exhaust is the way to go. The individual banks cannot induct properly, the pulses of exhaust gases are spaced to far apart. Duals works better on v8 engines. Go 2 1/4 on the 3.0

2 1/4 is a good size for the 4.0 as well.

And whichever way you choose, a converter is a must, you cannot get a good power output without one.

 

The reason, I'm asking is I had a duel setup with 2 inch. But I have to replace from the flex pipe back and am thinking of 2 1/2 " duel setup.

 

Well, replaceing the flex pipe will be no big deal, but let me make a suggestion. keep the system close to stock size. Improve the y-pipe, so that is doesn't fight itself. After the cat, you could them y- out to a dual type system. That should work very well, and yield the best performance at all levels. Dual exhausts do not work as well as people say. The worked much better on carbed systems. On FI, they almost always yeild a loss in average power.

 

What facts do you have on this?

 

Hello, I am an exhaust specialist. Let me explain how an exhaust system works.

The 4 stroke engine does not exist in any car on the market today. And engine can be broken into 8 distict phases. The exhaust valve opens before the end of the power stroke. The pressure is released, and the momentum of the gases rushing down the pipe creates vacuum in the combustion chamber, helping to scavenge all the exhaust gases out of the chamber. If the size of the pipe is too large, the escapeing gases will not have enough momentum to create this vacuum, so exhaust gases will remain in the chamber. This is especially true at low RPM. This effect gets worsened when FI is introduced, and here is why. When the pipe size is too small, cyclonic vortexes form in the exhaust system. These vortexes create pockets of gases that are incompletely mixed. The O2 sensor reads these gases, and yields incorrect reading, so the computer adjusts. The mixture changes, and the computer does not pick up on the changes till too long after the fact. At this point is correct, but over corrects. The computer will go through cycles or overcorrections, because the computer is not getting the readings of the current exhaust gases. The result is a overly rich average, and poor fuel economy, and reduced power due to running too rich.

The reason a dual exhaust worked better on carbed system, is because they didn't change their settings, or if they had computer management, they could change much or as quickly. As a result, you didn't get the lagging results.

You may now state that some cars come with dual exhausts. My responce is, they are tuned to run with those dual exhausts. The computer takes that into account, and the locations of the O2 sensors and converters is carefully thought out. Moving the sensors by as much as 1/2" can cause the above scenario. This is part of the reason it is illegal to change the location of an O2 sensor.

 

My system just won't rust out! I'd like to improve it but unless it fails and I need to replace it, I can't justify doing it. It would take a loooong time for a new system to pay for itself in fuel savings. The minimal power benefits don't justify it either.

 

I'm not talking true duel, just as you stated. I had it Y'd after the muffler. It worked greta. I gained a lil more power. As for moving the 02 sensor, I know if recaled for where it is it will work. A vehicle tech friend of mine, added a true duel exaust to his Explorer. He moved the cats to each side. It was a early 98, with 4 Cats. He went to 2, crossed over the headers and ran it back.
I think 1/2 bigger will work. I'm not looking for a tyre burner, just a lil power and looks. Here in Canada, there is no law about 02s, for only Southern Ontario has a ELaw. To pass a safety in NB, NS, PEI, just as long as it has 4 tyres, not holes in floor, all the lights work and no mechanical problems it passes. It could blow pink smoke and it will get it's sticker.

 

Ok, a y after the muffler should be fine, maybe even beneficial. If you wanted, I could also get you a nice high flow converter with stainless steel pipe and bodies for not too much. For mufflers, I recommend Magnaflo, Dynomax, or the Flowmaster 40 series. When you switch to a dual setup, the pipe size needs not step up, but you could put on a stainless steel tip that makes it look larger. dual 2" out the muffler would do nicely, then flair it to to 2 1/4" so that it can use standard sized stainless tips.